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aggregate virtiofs: share multiple Windows folders via a single device #40729

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19 changes: 17 additions & 2 deletions src/linux/init/WSLCInit.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@ Module Name:
#include "message.h"
#include "localhost.h"
#include "common.h"
#include "drvfs.h"
#include <utmp.h>
#include <unistd.h>
#include <sys/wait.h>
Expand Down Expand Up @@ -652,8 +653,22 @@ void HandleMessageImpl(
// Chroot without OverlayFs is not supported — the chroot logic depends on the overlay target path.
THROW_ERRNO_IF(EINVAL, WI_IsFlagSet(Message.Flags, WSLC_MOUNT::Chroot) && !WI_IsFlagSet(Message.Flags, WSLC_MOUNT::OverlayFs));

auto type = readField(Message.TypeIndex);
THROW_LAST_ERROR_IF(UtilMount(source, target, type, options.MountFlags, options.StringOptions.c_str(), c_defaultRetryTimeout) < 0);
const char* type = readField(Message.TypeIndex);
const char* subname = readField(Message.SubnameIndex);
if (*subname != '\0' && strcmp(type, "virtiofs") == 0)
{
//
// Windows-folder share routed through the single aggregate
// virtio-fs device: bind-mount the child identified by Subname
// instead of mounting a dedicated device. The helper re-parses
// the raw option string itself, so pass it through unparsed.
//
THROW_LAST_ERROR_IF(MountVirtioFsAggregateChild(source, subname, target, readField(Message.OptionsIndex)) < 0);
}
else
{
THROW_LAST_ERROR_IF(UtilMount(source, target, type, options.MountFlags, options.StringOptions.c_str(), c_defaultRetryTimeout) < 0);
}

// Workaround for a Linux bug where virtiofs permissions aren't properly propagated when an overlay is mounted on top of a virtiofs share before the permissions have been fetched.
// TODO: Remove once fixed upstream.
Expand Down
55 changes: 48 additions & 7 deletions src/linux/init/config.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1706,10 +1706,23 @@ Return Value:
while (MountEnum.Next())
{
//
// Do not consider bind mounts.
// Skip non-root mounts (bind mounts), with one exception: aggregate
// virtio-fs shares are always bind-mounts from the aggregate device's
// synthetic-root child, so virtiofs entries with Root != "/" are
// legitimate drvfs mounts whose subname is encoded in Root.
//

if (strcmp(MountEnum.Current().Root, "/") != 0)
const bool IsVirtioFs = (strcmp(MountEnum.Current().FileSystemType, VIRTIO_FS_TYPE) == 0);
if (!IsVirtioFs && strcmp(MountEnum.Current().Root, "/") != 0)
{
continue;
}

//
// The aggregate-device root mounts under VIRTIOFS_AGGREGATE_ROOT_DIR
// are internal infrastructure (not user-visible drvfs targets); skip.
//
if (IsVirtioFs && wsl::shared::string::StartsWith(MountEnum.Current().MountPoint, VIRTIOFS_AGGREGATE_ROOT_DIR "/"))
{
continue;
}
Expand All @@ -1732,9 +1745,15 @@ Return Value:
MountSource = MountEnum.Current().Source;
UtilCanonicalisePathSeparator(MountSource, PATH_SEP_NT);
}
else if (strcmp(MountEnum.Current().FileSystemType, VIRTIO_FS_TYPE) == 0)
else if (IsVirtioFs)
{
MountSource = QueryVirtiofsMountSource(MountEnum.Current().Source);
//
// For aggregate shares, derive the subname from Root (strip leading "/").
// Legacy direct-mount shares have Root == "/" → empty subname.
//
const char* Root = MountEnum.Current().Root;
const char* Subname = (Root && Root[0] == '/') ? Root + 1 : (Root ? Root : "");
MountSource = QueryVirtiofsMountSource(MountEnum.Current().Source, Subname);
}
else
{
Expand Down Expand Up @@ -2327,10 +2346,26 @@ try
//
// Bind mounts which have a root other than / are currently not supported.
//
// TODO_LX: Support bind mounts.
//
// Skip non-root mounts (bind mounts), except for aggregate virtio-fs
// shares which are themselves bind-mounts from the aggregate device's
// synthetic-root child. For those, Root encodes "/<subname>".
//
// TODO_LX: Support arbitrary bind mounts.
//

if (strcmp(MountEntry.Root, "/") != 0)
const bool IsVirtioFs = (strcmp(MountEntry.FileSystemType, VIRTIO_FS_TYPE) == 0);
if (!IsVirtioFs && strcmp(MountEntry.Root, "/") != 0)
{
continue;
}

//
// The aggregate-device root mounts under VIRTIOFS_AGGREGATE_ROOT_DIR
// are internal infrastructure (not user-visible drvfs targets); skip
// them so they're not torn down and remounted incorrectly.
//
if (IsVirtioFs && wsl::shared::string::StartsWith(MountEntry.MountPoint, VIRTIOFS_AGGREGATE_ROOT_DIR "/"))
{
continue;
}
Expand Down Expand Up @@ -2447,7 +2482,13 @@ try
}
else if (strcmp(MountEntry.FileSystemType, VIRTIO_FS_TYPE) == 0)
{
RemountVirtioFs(MountEntry.Source, MountEntry.MountPoint, MountEntry.MountOptions, Message->Admin);
//
// Derive aggregate-child subname from Root ("/<subname>", or "/"
// for legacy direct-mount shares).
//
const char* Root = MountEntry.Root;
const char* Subname = (Root && Root[0] == '/') ? Root + 1 : (Root ? Root : "");
RemountVirtioFs(MountEntry.Source, Subname, MountEntry.MountPoint, MountEntry.MountOptions, Message->Admin);
}
else
{
Expand Down
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